Test instrument for blind landing systems



Jan. 6, 1953 R. A. EMMETT, .1R

TEST INSTRUMENT FOR BLIND LANDING SYSTEMS 5 Sheets-Sheet l Filed Nov. 26, 1945 ROBERT A. EMMETT JR.

Jan. 6, 1953 R. A. EMMETT, JR

TEST INSTRUMENT FOR BLIND LANDING SYSTEMS 5 Sheets-Sheet 2 Filed Nov. 26, 1945 WR. J Tl MT qlmvE M M E A. T R E B O R Jan. 6, 1953 R. A; EMMETT, .IR

TEST INSTRUMENT FOR BLIND LANDING sYsTEMs Filed Nov. 26, 1945 5 Sheets-Sheet 3 ROBERT A. EMMETIJR.

Jan. 6, 1953 R. A. EMMETT, JR

TEST INSTRUMENT FoE BLIND LANDING SYSTEMS 5 Sheets-Sheet 4 Filed Nov. 26, 1945 mmmJDa .FDLPDO kwh.

me/YM ROBERT A. EYMMETT JR.

JNL 6, 1953 R. A. EMMETT, .1R 2,624,872

TEST INSTRUMENT EUR BLIND LANDING SYSTEMS Filed NOV. 26, 1945 v5 Sheets-Sheet 5 lume/wm ROBERT A. EMMETT JR.

LEFT OUT RlGHT OUT Summen;

Patented Jan. 6, 1953 UNITED STATS PATENT OFFICE TEST INSTRUMENT FOR BLIND LANDING SYSTEMS Robert A. Emmett, Jr., United States Navy Application November 26, 1945, Serial No. 630,958

This invention relates to test instruments and, more particulariy, to an electronic device for use in conjunction'with the airborne components of a blind landing'system to generate artiiicial position and course deiining signals and test the response of the airborne component thereto.

This test unit is particularly designed to operate in conjunction with the system described 1n the copending application of T. R. Burnight et al., Serial No. 629,688 filed November 19, i945 for a Blind Landing System. This system involves a ground installation which, upon being challenged by echo ranging apparatus in an aircraft, radiates lobe-switched pulses from a pair of directional antennas, to denne by the radiation field then produced, the position of the runway and the proper course path to eiect a blind landing thereon. To sense these radiations and to provide indication in the aircraft of the axis ci the runway and of the position of the aircraft, a receiving unit is provided in the. aircraft comprising a dual-channel receiver and sensing unit, the channels of the receiver 'being coupled each to a directional receiving antenna at each side of the center of the aircraft and the sensing unit having timing and measuring circuits to compare the output of the two receiver channels and convert the comparative amplitude into a meter ndication of the crab of the aircraft, i. e. relative heading of aircraft with respect to the bearing of the source of ground radiations, to compare the amplitude of the two radiated fields and indicate the equi-signal path defined by the two lobes and to sense the time occurrence of the pulses and indicate therefrom the range of the runway from the aircraft. To artificially generate and supply to this airborne component pulses manually controllable to simulate various ranges, course paths and crab" headings in the receiving unit and to mix artificial interference radiations with these signals to determine the effect of interfer ence on the system, the instant test instrument is designed.

Accordingly, it is an object of this invention to provide a novel test instrument for use in conjunction with a blind landing system.

Another object of the invention is to provide a test unit adapted to be used with an airborne position sensing component of a blind landing system to artificially generate signals such as those set up by the ground installation of a blind landing system to define the approach path to the runway Another object of the invention is to provide a test instrument adapted to be used with the airborne components of a blind landing system, the test instrument being manually controllable to simulate various known ranges, course paths and angles of bearing to calibrate the sensing circuits of the airborne components.

Other objects, advantages and capabilities of the invention will become apparent from the 'following description taken in conjunction with the accompanying drawings, showing only a preferred embodiment of the invention, in which:

Fig. 1 is a block diagram of the pulse circuit component of the instant test instrument,-

Fig. 2 is a block diagram of the position simulating circuit component of the instant system;

Fig. 3 is a schematic diagram of the puiser circuit component;

Fig. 4 is a schematic diagram of the manually controllablecomponents of the simulating circuit;

Fig. 5 is a schematic diagram of the output circuit coupled to the position simulating circuit unit.

Referring now to Fig. 1, showing the block diagram of the pulsing unit, synchronizing signals generated by any conventional form of synchronizing pulse generator are fed into a synchronizing amplier Ill. These synchronizing pulses are employed to synchronize the test unit with a standard synchroscope so that waveforms tapped off at various points in the test unit may be observed thereon. The output of the synchronizing famplier I0 is fed into a repetition rate multivibrator II which is manuallyv controllable' to simulate the pulse repetition frequency of a conventional echo ranging unit. The square Wave output Aof the repetition rate multivibrator II is fed to an amplifier and peaker I2 which peaks the leading and trailing edges of the squarewave output of the repetition rate multivibrator II to produce a series of positive and negative pulses. These pulses are coupled to a pulse width multivibrator I3 which is manually controllable and triggered by the positive pulses produced in amplifier I2 to trigger the pulse width multivibrator I3 and generate a positive pulse which is a reference pulse of a duration determined, by the setting of the manual control coupled thereto. This pulse output is coupled successively through yan amplier I4 and a cathode follower I5 from which the pulse may be tapped off and applied to the receiving unit of the blind landing system. This reference pulse of controllable repetition frequency serves as the cycle initiating pulse for the receiving and 'sensing units. The series of positive and negative pulses generated by amplifier I2 are also fed to a first sliding pulse strip, the input stage of which is a delay multivibrator l which is manually controllable to insert a predetermined amount of delay in its output trigger pulse with respect to the time of occurrence of the input pulses. These output pulses are coupled through a differential amplifier Il to a pulse Width multivibrator stage I8 which is also manually controllable to generate a pulse of predetermined duration when triggered by the output of amplier I1. The pulse output of the pulse width multivibrator i8 is then coupled through an amplifier i9 and cathode follower stage 28 to a mixer stage 21 from which the pulse may be coupled into the receiving unit of the blind landing system. The pulse output of amplifier l2 may also be coupled into a second sliding pulse strip, the input stage of which is another manually controllable delay multivibrator 22. This stage, as in the case of the delay stage le in the first sliding pulse strip, is designed to introduce a selectable amount of delay into output trigger pulses with respect to the input pulses. The delayed pulse output of the delay multivibrator stage 22 is fed through a differential amplifier 23 to a pulse Width multivibrator 24 which is likewise manually controllable to enable variation of the pulse width as desired. The pulse output of the pulse Width multivibrator 24 is coupled through an amplifier 25 and a cathode follower stage 26 to the mixer stage 21, from which the mixed pulses generated in the two sliding pulse strips may be picked oi and coupled to the receiving unit of the blind landing system. The variable delay and variable width pulses generated in this pulser circuit may be coupled from the mixer stage 21 above mentioned into the position simulating circuit shown in Fig. 2. This position simulating circuit enables a successive group of pulses picked off of the pulsing unit to be timed and shaped to simulate the range position of the aircraft, the relative bearing of the aircraft, and the proper approach path of the aircraft with respect to a runway.

Referring therefore to Fig. 2 showing a block diagram of the position simulating circuit, I have provided a free running multivibrator 28, the switching period of which is manu-ally controllable to simulate the antenna switching frequency of the antennas of the ground installation of the blind landing system. The output of the free running multivibrator 28 is then coupled into an electronic switch 29 designed to produce a nat-topped gating signal to alternately gate a pair of clipper amplifiers 33 and 3l. The output of the free running multivibrator 28 is also coupled through an automatic-servo switch 32, when it is desired that the system operate on automatic, to a pair of gating multivibrators 33 and 34. These gating multivibrators 33 and 34 are alternately triggered to produce negative gates to cut off current flow in oscillators and 36. Since the oscillators 35 and 36 are designed to oscillate at different natural frequencies and generate a series of modulated synchronizing sigals, the alternate gating of multivibrators 33 and 34 produces alternately different frequency outputs from the oscillators 35i and 36 which are coupled into a mixer stage 31 where the modulated signals generated by the oscillators 35 and 36 are mixed with the signal coupled from the mixer output terminal of the pulser unit previously described. The frequency modulated pulse output of the mixer 3l is then coupled into the gated clipping -ampliers 38 and 3l. The clipping amplifiers 3@ and 3l are manually controllable to limit the amplitude of the pulses fed there- Clt ' T. R', Burnight et al.

' sistor Hi8.

4 through during the period when these amplifiers are conducting to simulate various amplitudes of pulse radiation, thus effectively varying the simulated equi-sign-al path. The gated outputs of the clipping ampliiiers 30 and 3| are then coupled into a mixer 38 Where the outputs are mixed in proper time relation and thence fed to gated clipping ampliers 39 and 40.

The gating signals for the clipping amplifiers 3S and 40 are generated in the following manner. A free running multivibrator 4I is pro vided, the free running period of which is designed to simulate the antennav switching frequency of the airborne unit. The output of this free running multivibrator Ill is then coupled into an electronic switch 42 to produce a gating signal synchronized with the multivibrator output for gating the clipping amplifiers 39 and 40. The clipping amplifiers 3S and Lil) are also manually controllable to limit the amplitude of the pulses fed therethrough to simulate various amplitudes of pulse signals picked up by the directional receiving antennas carried by the aircraft. and thus simulate the relative bearing of the aircraft with respect to its line of bearing from the runway. rlhe outputs of these clipping ampliiiers 39 and 4G are then coupled through a series of amplifier stages 43, 44, 45 and 46 into cathode followers i1 and d8, respectively, from which the pulse outputs cf the two channels. can be picked off and coupled into the video signal input channel of the receiving unit of the blind landing system.

By means of this position simulating circuit, control of the timing of alternate groups of pulses of predetermined width determined by the setting of the manual control in the pulser circuit has been provided to simulate the antenna switching characteristics of a ground approach path defining system. Likewise, means have been provided for varying the relative amplitude of alternate groups of pulses so that the aircraft may appear to be at various positions away from the equi-signal path of the radiation iields generated by the ground radiation. By means of the free running multivibrator 4l and the clipping amplifiers 39, 48, the relative amplitude and timing of groups of pulses in the receiver are effectively varied to simulate various orientations of the pair of receiving antennas into which the ground radiation patterns would be coupled, with respect to the hypothetical source of radiation and its bearing from the aircraft, and also the antenna switching frequency of the airborne unit. It should be noted -that the clippers 39 and4 4U are designed to have relative transfer efficiencies equal to the relative eld strengths of the,

pair of antennas of the system disclosed in the previously mentioned copending application of These transfer efficiencies are measured along a line extending between the airborne yand the ground-located pairs of antennas when the aircraft equipment is in a simulated position.

Referring now to the specific circuit details through which the position simulating circuits eiect control. of the repetition frequency and time delay of the pulses in the pulser unit, shown in Fig. 3, synchronizing pulses are coupled through condenser lill -to the grid I 02 of tube 63 forming the synchronizing amplifier I6. The pulse output of the tube HB3 is coupled from the plate idd and cathode M5 thereof through condensers 18S and H31 to a center grounded re- Thus a signal of desirable ampliacca-8va tudeand polarity fmaybe lpicked. off ".romfth movablel arm of the :potentiometer .-15118 landhad synchronizing pulsesare then coupled. .from the plate I tof' 'the `amplifier 0 through :coupling condenser H2 -to fthe :grid 1||3 of tube y'H4 -inithe repetitionl yrate -multivibrator circuit 4H.. Tubes Ilfkl and f|.|'5 are interconnected #to form :a -cone ventional rgridepl'ate .coupled multivibrator.; To provide .manual .control of 'the switching .period of. this multivibrator,l 'the grid H13-fof tube 'Ill 4 vis connected through :a :dropping :resistor ,1| |:6 to thel variable :arm :of potentiometer |.'|1 having .a D. .voltage applied l-therea-cross.. Likewise the grid HB .of tube |115 `is coupled through a drop-` ping resistor. |118 ltothe movable :arm vlill) of an fautomatic-fservo..'switch. The ,movable arm f| 2|] oft'the. ffautomatic-servo" switch is'adaptedto engagethe switch terminal :i 21| when in "automatic1L position to couple the resistor H9, and thus. the .fgrid Lil-*8, te .the movable :ar-m of. the potentiometer M1. When in servo yposition., thermo-Vahle arm |26 rofthe switch is f'adaptedfto engage ya switch Acontact :|22 which couples the. lgrid .|18 directly to ground instead of to` `the D. C. potential determined by `the setting of `the potentiometer arm I1. rlI'h-usby variation-of the position of lthe .arm 'of rpotentiometer H1., and thus the D. fC. potential tapped :om the switch-v ing .period Aof the multivibrator is thereby ymade to simulate the pulse repetition frequencyof the ground installation. Thesquarewave .output 'of the repetition rate multivibrator .is Vcoupled from thejfplate ,|23 oi tube |.5throughan 1R. C. peaker circuit comprising condenser |24..and .resistor |25 to 'the grid. 26 oftube I 21 forminga conventional amplier istagge. The amplifier output, .comprising `a .series of positive and .negative .pulses cor.- responding .in-time to .the .switching points of multivibrator il., is coupled from the plate. |28- of .'amplier `'|21 througha .coupling condenser. |29 .to the input fgrid |30 .of the pulse Width multivibrator .comprising tubes 139|, |52., and .|33 interooupled as a, cathode coupled multivibrator. The plate |34. of tube ,|.3| is .coupled directly to the plate. |35 of tube .|32 and through .a coupIirigcOndenSery |36 to the grid. |31 of tube |33. The vgrid .138..of tube |32 inv the multivibrator circuit .is coupled directly to l.the movable' .arm 1.3.9 of .potentiometer |41! .connected `across a D; C. .voltage inseries with 'resistors |`4| .and |42. This .potentiometer |46 providesy a means of. manually. .regulating the D. Cfbiasxvoltage on the .grid |38 of tube '|32 Vand thus. the `retriggering point of that tube i. e. vthe point at which tube |32 l.cuts off after 'it is caused to conduct-by the initiatingv pulse. 'Thisstage provides variation of the delay .inserted vbetween the time of occurrence of the positive trigger pulses on the grid 136101 tube |3| andthe trailing edge .of the negative output at the plate '|35' of tube |32. The pulses of selected Width .occurring at the plate |35 of tube |32 are coupled through a coupling condenser |43 to the grid |44 of'a p'entode amplifier |45. vThese pulses are merely amplified and inverted by the pentode '|45 and VAcoupled from the plate VH thereof through condenser '|41- to the grid |48 of the cathode follower voutput tubey |49. The cathodev |5 of tube |49 is coupledv to groundy through va potentiometer |51. Thus the amplitude of the pulses cou-pled from the movable'army |52 of potentiometerv -|5| may be controlled by varying the position of the arm |52. The pulses coupled out of output terminal 1.53.!na'y be employedto synchronizethe receiv 6. ing and indicating unit ofthe .blind 'landing .sys-

tem or'of'aitest synchroscope to Iprovide a proper;r

time base for measuring the pulses.

vThe vpulses atfthe plate |28 of amplifier .tube |21 fare likewise coupled through coupling -'cons denser |5'4to'the input grid |55 'of the pulse delay multivibrator |"6 made upfof tubes |556, |51,-and

|f58 interconnected as a f'catho'de coupled multi"hv vibrator. This delay. rnultivibratorY circu-ituis identical in .its lin'terconnection to the pulse'width multivibrator foire-uit previously described, 'withV thepl'ate |J5`f9..o'f'-tube |`561rcoupled ydirectly to the plate BOaofratube |51 :and through condenser/|61-v tothegrid v|1612 oftuhe 58.v Likewise, the Vgrid 163 ofitube lrlil'isfcoupled :directly to themovabl'e arm F64 .and potentiometer 465 `connected between-the positive D. C. plate supply volt-a'ge'and 'ground through fseriesuresistor l|655. The potentiometer |65 is'zprovided to make possible :manual'control ofthe Duc. bias level-on the grid |63 oftube |51.

and theinterval `forwhic'h the tube |51 :is cut o and thus the 'duration -of the `posi-tive pulse *produced `'on the plate +60; YThe trailingv edge ofthis positive'pulsef-is peaked by-a short time constant input circuit in the :succeeding stage to produce a .negative pulse coincident therewith. Thus va manually controllable ldelay is inserted .between the time occurrence of the pulses fed to the rgrid. of tube v|5| and lthe negative pulses. This delayed pulse is ycoupled through condenser |5651 tothe grid |458y of ampl-ierftube .163. The ampli-y fied and inverted pulses occurring at the. plate |1 -of the :amplifier |69 arethen coupled through condenser |1.| to vthe grid .|12 .of tube -|13..forr.f1ing vanother amplifier stage.

The .highamplitude .pulse output .from the .plate |14 .of amplier- |13 is coupled through `aA condenser |15 .to .theinput grid 15 of .the pulse with multivibrator I8. iDue tothe time constant of vthe multivibrator `|3 above described. The grid |80 .of -the second .tube |18of the `pulse/width multivibrator |.8 is coupled directly to the movablearm. of potentiometer |582 connected Ibetween .the D; C..

plate supply voltagev andground throug'hiD.. C; resistors |83.' This potentiometer. .|82 providesA manual control of the D'. C. bias voltage of the.

` grid |80 of tuber |18 'and thus thecutoi period of. tube `|19` when triggered by the delayed pulse.

Since the Waveiormcoupled .from the plate ,|84 of tube |11 to the grid "|85 of multivibrator-out-V put tube .|19 is a diieren'tiated pulse, the D. C. bias voltage on .the grid lill) of tube |18 determines the interval .of time that lwill elapse be. tween the Aleading edge of the pulse. to .plate |84h and the point at which the tube |19 afterbeing cut off by the leading edge of the diiierentiated pulse, again beginsto conduct, thus determining the pulse Width. The pulsegenerated at the grid |85 .of tube |19, the durationof which is manually determined, is coupled through the condenser |86'to the grid |81 of v.pentodeanipliter tube |83. The ampi-ined and .inverted pulse outputfrom the plate |89' of pentode |88 lis then coupled through' condenser |511! to the grid |91of pentode |92-conpied as a cathode follower. The cathode '|93 of pentode |92 is coupled to ground through' a potentiometer |94, the variable arm E95 of which is connected to terminal |96 from'which a pulse of varying tamplitude can be picked o by 7 varying the position Iof potentiometerarm |95 and fed through condenser |91 to the grid of triode |93 in the mixer stage 21.

The pulse output of the pulse amplifier |21, taken from the plate |28 thereof, is likewise coupled to the contact terminal 20| of the selector switch 2|. When it is desired to delay the pulses in the second sliding pulse strip with respect to the initiating pulses from amplifier |21,`the movable arm 203 coupled to the input grid 205 of the second pulse strip is positioned to engage switch contact 20|. When it is desired, however, to delay the pulses in the second pulse strip with respect to the delayed pulses in the first pulse strip, the movable arm 203v of the selector switch is positioned to engage a contact 202 which couples the initiating pulses for the second sliding pulse strip from the plate |14 of differentiating amplier |13 through the switch arm 203 to the grid 205 forming the input grid ofthe pulse delay multivibrator 22. This pulse delay multivibrator, identical in interconnection to the pulse delay multivibrator I3 above de scribed includes tubes 20B, 201, and 200. The grid 209 of tube 201 is coupled directly to the movable arm of potentiometer 2 l0 connected between the D. C. plate supply voltage and ground through series resistance 2||. This potentiometer 2 I0, as potentiometer |65, is provided to enable manual control of the delay ofthe initiating pulses fed to the grid 205 of tube 206 to be effected in a well known manner, The trailing edge of `the pulse generated at the grid of tube 208 in the multivibrator delay circuit is peaked to form a positive pulse by the input circuit of the next stage and is coupled to the grid of differentiating amplifier 2 I3. The differentiated pulse produced thereby is coupled from the plate 2|4 through condenser 2|5 to the input grid 2|3` of pulse width multivibrator 2 4. The pulse width multivibrator 24 is likewise identical to the pulse Width multivibrator |3, and includes tubes 2,|1, 2|8 and 2|9. The grid 220 of tube 2|8 is coupled directly to the potentiometer arm 22| of potentiometer 222 connected between the D. C. plate supply and ground through series .resistor 223. Thev potentiometer 222V is provided to 'enable manual control of the duration of the delayed pulse output of tube 2 I3 by controlling the period of conduction of tube 2|3. The pulse of desired width thus appearing on the plate 224 of tube 2|9 is 4coupled through condenser 225 to the grid 226 of amplifier 221 and thence from the plate 228 thereof through condenser 229 kto the grid, 230 of pentodeY amplifier 23|. The twice amplified p ulse is then coupled from the plate 232 of tube 23| through condenser 233 to thel grid V234 of pentode 235 connected as a cathode follower circuit. The cathode 236 rof cathode follower tube 235 is coupled to ground through potentiometer 231, the variable arm 238 of which is coupled through condenser 239 to the grid 240 of tube 24| which, together with tube |98, forms the mixer stage 21. Here the slidingpulse output of the second sliding pulse strip is mixed with the pulse output of the first sliding pulse stripin the common cathode resistor 200 coupled tothe cathode 242 of tube 24|I and cathode |99 of tube |98. TheA mixed output of both. pulse strips is taken olf at the upper end of the common cathode resistor 200 and applied to the pulser output terminal 243 from which the delayed pulse output is then coupled to the position simulating circuits to be now described.

Referring noWrto Fig. 4, in which are shown the circuitfretails by which the timing and shaping of the pulses are accomplished to simulate the various timing characteristics eiected in the ground installation and thelposition and range characteristics of the pulses due to the position of the aircraft with respect to the ground installation. The free running multivibrator 28 comprises tubes 30| and 302 which are so interconnected as to form a conventional grid-plate coupled multivibrator. of tubes 30| and 302, respectively, are coupled to ground through variable resistors 305 and 305 and center tapped resistor 301. The variable resistors 305 and 306 provide manual control of the free running period of the multivibrator to simulate the various antenna switching frequen# cies which may characterize a ground installa'- tion.

running multivibrator are coupled through condensers 3| 0' and 3H, respectively,to the grids 3|2 and 3|3 of tubes 3|4 and 3|5 interconnected to form an electronic switch. The output wave'- orms'of the multivibrator are peaked by re'-E sistor-capacitor combinations formed of `the condensers 3|3 and resistor 3|6 coupled to the' grid 3|2 and condenser'3llv and resistor l`3|1f the clipper amplifiers 30 and 3| shown at Fig.' 2.f'

This gating waveform is coupled from movable taps 323 and 324 at resistors 3|6 and 3|1 to pick,

off the desired amplitude of the gating pulse and feed through dropping resistors 325 and 325 to the grid 321 and 323 of clipper tubes 32| and 322. The vlobe-switch simulating trigger waveform in the multivibrator 28 is likewise coupled from the grids 3|2 and 3|3 of electronic switch tubes 3|4 and 3|5 to terminals 329 and 330 of the automatic-servo switch 32. The terminals 3,29 and33|l are adapted to be engaged by the movable arms 33| and 332 "of the automatic-servo switch to couple these triggers to the gating multivibrators 33 and 34. Additional switch terminals 333, 334 are positioned to be selectively engaged by the switch arms 33| and 332 when in. servo position to synchronize the` system with exterior generated synchronizing pulses. The trigger pulses coupled from the movable arms 33| and 332 of switch 32 are fed to the' plates 335 and 333of tubes 331 and 330 in thel multivibrator gatingcircuit 33 and 34. Thetubes 331 and 339, forming the multivibratorgate generator 33, arel interconnected as a convention grid-plate coupled multivibrator, as are the tubes 338 and 34|),forming the multivibrator 34. The grids 34| and 342 of tubes 339 and 340 are coupled to ground through variable resistors 343 and 344 to provide manual control to the switching periods .of the multivibrator and thus the time duration of the output negative pulses on the plates 335 and 336. These negative output gating pulses are coupled from the plates 335 and 336 through coupling condensers 345 and 345 vto the grids 341 and 348 of oscillator tubes 349 and 350. These oscillators are the conventional shock-excited type having tuned tank circuits comprising coils 35| and 352 and condensers 353 and354 coupled between'their cathodes 355 and The grids 303 and 304 The output waveform at the plates 301|'l and 309 of tubes 30| and 302 forming the free ldensers:380 and 38 I 9. 3.56,: respectively, and ground. vDirectly coupled tothe cathodes 355 and 356 ofA thev tubes 339. and 350 are. grids 351 and 35E- oi tubes 3.58 and 350. The cathodes of the tubes 353 and 330 are coupled to a center tap on the coils 35| and 352 through resistors. 333 and 333l and condensers 355 .and 366. Due to the feedback action in the cathode circuit of the tubes 359 and 330, the amplitude of the oscillations in the oscillator tank circuit is*A maintained substantially constant. Oscillator tubes 343 and 350 are normally conducting quite heavily. The negative pulse generated at one oi thev plates 335, 336 of tubes; 331. and 33B when one. of the multivibrators is' triggered cuts oi one of. the oscillator tubes 349 and 353 and shock excites one. of the coils 35| and 352. TheY suc.- ceeding oscillations are coupled from the cathodes 36| and 332 of feedback tubes. 359 and 360 through. coupling condensers 331 and 368 to the grids 369, 318 of ampliiier tubes 31| and 312,

the cathodes of the amplifier tubes 31|' and 312 `being coupled through a` common cathode potentiometer 3.13 to ground. The Variable arm of. this potentiometer 3? 3 couples a variable amplitude of thesynchronizing signal through a coupling condenser 314' tothe grid 3150i tube 313, one of the twotubes in the mixer stage 31. The output -signal of the puiser circuit component shownin Fig. 1 is coupled into an input terminal 311 from lwhich thepulse signal is fed through a coupling condenser 313 to the grid 319 of the tube 380, the other tube in mixer stage 31. The cathodes of `the tubes- 315 and 380 are coupled to ground through a common resistor 38 l, inwhich the synchronizing signals at the two modulation frequencies are mixed with the pulse output of the puiser unitY to provide pulses" mixed `in' proper time relationwithsynchronizing signals such' as would bel present in the received radiations of 'the ground installationV of the blind; landing system. These alternately modulated signals and pulses in the commonV cathode `resistor 38| are also lcoupled to the' grids 321 and' 328 of the clipper tubesV 32| andV 322i through: coupling contiometers 3.82l and'l 383*4 to ground'. The'variable `armsof thep'otentiometers 382 and" 383 are ganged together to provide simultaneous manual operationand the signal i's coupled therefrom through condensers 384'and 385 to the grids of mixertriodes 386 and 381; The potentiometers 382 and' 383 form 'the manualv course` con- `trol by which the relative amplitude of the gating signal 'outputA of" the. clippers. 321| and 322 may bev varied". to simulate. the. iield strengths. which 'would be experienced at' various points away 'from an equi-signal line of the switched lobes radiated'by the ground approachpath. dening system., The cathodes of the mixer tubes. 386

and 381`are, coupled. to ground through acommon cathode resistor` 388. Likewise coupled to.. the

' top of the common cathode resistor 388 are the cathodes of. mixer tubes 389.- and 39.0 into. the grid of..which. may beselectively introducedvariousamplitudes of. interferencesig-nals.- whichiv may be-.mixed with the course deninggpulsesnto simulate. various atmospheric .and spuriouswinterferenceswhichmay. be experienced in the reception. of; theground. radiated, coursei defining.. signals.. The. mixed interference and coursedening, pulses are then coupled'. from, the: top of the, common.. cathode.` resistor- 38.8r through;v coulpling.,condensers39|.F and1392 torclipper triodes;v

Theicathodes'of the'triode ,clippers 32| and 322v are coupled" through poten- 10 3:93 and 3.93. To simulate the gating frequency of the video switch, in the dual channel receiving unit of the airborne echo-ranging unit ofthe blind landing system,4 a-fmultivibrator comprising tubes 39,5. and 39.3- i-s.. provided, the tubes 3351 and 303 being coupled together asa convention grid-plate coupled multivibrator. The grids cf the tubes 395. and 393;.arev coupled toground through variable potentiometersv 331 and 308.. The. variable arms of potentiometers V353-1 and 3381,'coupled. between the grids of the freeI running multivibrator tubes 335 and336, are coupled together toprovide accurate manual -control of the switching period of the multivibratorsf,v designed simulate the switching period ofV the receiving antennas coupled to the dual channel receiver in the airbornel unit of the blind landing system. The switching waveform at the plate .of the; tubes 335y and 3.36 is coupled. through condensers 399 and. 400- to the grid of triodes 40| and-.482 .forming an electronic switch for.. pro.- ducing: afla-ttopped gating pulse for the clipper amplifiers 393 and .394. The triodes 40| and 402 arel intercoupled as conventional electronic switch stage with thefresistor-capacitorA networks 433, and. 4M: coupled between. the plate of one tube andv the.- grid=-of the opposing tube in the .pair forming the electronic switch. Variable potentiometers 405 and 406 are coupled `between the grids of the triodes 40| and. 402 and ground, respectively.. The movable.- arms of the. potentiometers 435 and 306 are coupled through dropping. resistors to the; grid of the clipper: triodes 383 and 394.y Thus by variationof the position of themovable.y arm on the. potentiometers 405 and 406the'desiredamplitudeof the alternating, gating Waveform generated by the electronic switch. d2 may be picked. 01T and fed to the grids of the tubes 333 and 334. thus gating themalternatelyy tol simulate the switching of the channels of. the dual .channel receiver inthe blindlanding system..

Thecathodes of the gated clipping triodes are coupledthrougm variable potentiometers 40.1 and 4.0.3. to ground,v the movable arms of which are ganged and manually controllable. to alter the relative. amplitudes; of; the alternately gated pulsesto simulate various angles of orientation of. .thef receiving,E antennas in the. airbornefcomponent, of the blind; landing system. with respect to the. simulated .source of.. ground radiation. The position simulating pulses generated by the circuit.- components just described are.v tapped fromthe movable arm of thepotentiometers 4.01 and 408. and fed to theseparate channel output stages shown in Fig. 5. Thepulses coupled from the variable armof. the. potentiometersv 401 and f llare fed throughcoupling condensers 409 and 410, shown. in Fig.. 5,4 to the. control. grids of The. outputs. ofY the of another pair of pentode .amplifiers 4|1..and 4|8. The: twice,v amplified pulses are coupled fromA the plates. of; the. amplifiers 4|1 and '418 throughv coupling, condensers, 42| and 422;to1the control grids` of pentode cathode: followers-423 and 324. These. cathode. .followers 423.an.d-.424 form.V the outputstagesqfor the pulseszfrom each gated. channel, the .cathodes of the amplifiers 23l and 424y being coupled to groun'dt. through variable potentiometers 425 and 426.. Thus. a variable. amplitude; pulse may be coupled vfrom the. movable. arm.- of. the potentiometers'r425. and

226 in the cathode circuit of the cathode followers to the output terminals 421 and 428, so designed as to simulate the pulses which would be present in the output of the receiver channels associated with the right and left antennas of the airborne component of the blind landing system.

In the two circuit units just described, we have thus provided manual control means for spacing and shaping the individual pulses generated in the pulser units in accordance with the various amplitude and time characteristics which would be imposed upon the pulses at various positions in the radiated fields generated by the ground installation of the blind landing system. It will be apparent that coupling of the pulses from the output terminals 421 and 428 to the input terminals of the sensing circuit in the airborne component of the blind landing system above referred to will provide calibrated pulses by which the accuracy and response of the airborne sensing unit can be tested, and by which the various metering circuits in the sensing unit for indicating course bearings, deviations from on course path, range, and the course of the aircraft may be accurately calibrated. Thus neither the cumbersome ground installation nor actual field test procedure are required to effectively test and calibrate the receiving unit.

Various modifications may be made in the invention without departing from the spirit and scope thereof.

The invention described herein may be manufactured and used by or for the Government of the United States of America Without the payment of any royalties thereon or therefor.

What is claimed is:

1. Apparatus for simulating the video pulses obtained in the receiver output of a blind landing system utilizing an airborne pulse-transmitting and echo-receiving means including a first pair of directive receiving antennas having overlapping eld patterns alternately connected to the radio receiver means and a ground located transmitting means triggered by the airborne transmitter having a second pair of directive antennas also having overlapping field patterns a1- ternately fed with pulses of energy. comprising the combination of a first means for generating and initiating reference pulses of variable pulse repetition frequency, second means coupled to said rst means operative in response to one of said reference pulses to generate at least one pulse having a variable time relation with said reference pulse in accordance with the simulated range position of the aircraft, generator means for generating a pair of time displaced signals each of which have different frequency characteristics, first mixing means coupled to said generating means and to said second means for mixing the outputs thereof, second mixing means coupled to said first mixing means for periodically varying the output signal received from said first mixing means between two amplitude levels, the relative amplitude levels being proportional to the relative field strengths of said second pair of antennas as would be measured at the simulated aircraft position, third and fourth means coupled to said second mixing means having relative transfer efficiencies equal to the relative field strengths of said first pair of antennas when measured along a line extending between said first and second pairs of antennas when said aircraft is in said simulated position, switchingl means coupled to said third and fourth means for making said third and fourth means alternately operative to couple the input pulses to the outputs thereof, the respective outputs of said third and fourth means simulating the pulses of energy which would be detected at the output of the respective antennas of said first pair of antennas.

2. Apparatus for simulating the video pulses obtained in the receiver output of a blind landing system utilizing an airborne pusle-transmitting and echo-receiving means including a first pair of directive receiving antennas having overlapping eld patterns alternately connected to radio receiver means and a ground-locating transmitting means triggered by said airborne transmitting means having a second pair of directive antennas also having overlapping eld patterns alternately fed with pulses of energy, comprising the combination of first means for generating and initiating reference pulses of varia'ble pulse repetition frequency, second means coupled to said first means operative in response to one of said reference pulses to generate at least one pulse having a variable time relation with said reference pulse in accordance with the simulated range position of an aircraft, mixing means, third and fourth means coupled to said mixing means having relative transfer efficiencies equal to the relative field strengths of said second pair of antennas measured at said simulated aircraft position, switching means coupled to said third and fourth means for alternately rendering same operative to couple the input pulses to the output thereof, fifth and sixth means each coupled through said mixing means to said third and fourth means having relative transfer efficiencies equal to the relative field strengths of said first pair of antennas when measured along a line extending between said first and second pairs of antennas when said aircraft is in said simulated position, switching means coupled to said fifth and sixth means for making same alternately operative to couple the input pulses to the outputs thereof, the respective outputs of said fifth and sixth means simulating the pulses of energy which would be detected at the output of the respective outputs of said first pair of antennas.

3. The combination of a first means for continuously producing a series of pulses, second and third means coupled to said first means each having variable transfer efficiencies, mixing means, switching means coupled to said second and third means for alternately rendering same operative at a first given rate to couple the input pulses to the outputs thereof, fourth and fifth means each coupled through said mixing means to said second and third means each having variable transfer efiiciencies, switching means coupled to said fourth and fifth means for alternately rendering same operative at a second rate different from said first rate to couple the input pulses to the outputs thereof.

4. The combination of a first means for continuously producing a series of reference pulses of variable pulse repetition frequency. second means coupled to said first means operative in response to one of said reference pulses to generate at least one pulse having a variable time relation with said reference pulse, third and fourth means coupled to said second means each having variable transfer efiiciencies, a mixer, switching means coupled to said third and fourth means for alternately rendering same operative at a first given rate to couple the input pulses to the outputs thereof, fifth and sixth means each coupled through said mixer to said third and fourth means each having variable transfer efficiencies, switching means coupled to said fifth and sixth means for alternately rendering same operative at a second rate different from said first rate to couple the input pulses to the outputs thereof.

5. The combination of a first means for continuously producing a series of pulses, a second i and third means coupled to said rst means each having variable transfer efficiencies, switching means coupled to said second and third means for alternately rendering same operative at a iirst given rate to couple the input pulses to the outputs thereof, fourth and fifth means each coupled to said second and third means each having vari able transfer efliciencies, switching means coupled t0 said fourth and fifth means for alternately rendering same operative at a second rate different from said first rate to couple the input pulses to the outputs thereof, a mixer, said second and third means being connected to said fourth and fth means through said mixer.

6. Apparatus for simulating the,video pulses obtained in the receiver output of a blind landing system utilizing an airborne pulse-transmitting and echo-receiving means including a first pair of directive receiving antennas having overlapping fleld patterns alternately connected to the radio receiver means and a ground-located transmitting means triggered by the airborne transmitter having a second pair of directive antennas also having overlapping eld patterns alternately fed with pulses of energy, comprising the combination of a rst means for continuously producing a series of reference pulses of variable pulse repetition frequency, second means coupled to said first means operative in response to one of said reference pulses to generate at least one pulse having a variable time relation with said reference pulse, third and fourth means coupled to said second means each having variable transfer eiciencies, switching means coupled to said third and fourth means for alternately rendering same operative at a first given rate to couple the input pulses to the outputs thereof, fifth and sixth means each coupled to said third and fourth means each having variable transfer efficiencies, switching means coupled to said fifth and sixth means for alternately rendering the same operative at a second rate different from said rst rate to couple the input pulses to the outputs thereof, a mixer, said third and fourth means being connected to said iifth and sixth means through said mixer.

ROBERT A. EMMETT, JR,

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,181,568 Kotowski Nov. 28, 1939 2,262,838 Deloraine Nov. 18, 1941 2,373,145 Sensiper Apr. 10, 1945 2,401,432 Luck June 4, 1946 2,440,261 Ginzton Apr. 27, 1948 2,493,774 Moore Jan. 10, 1950 2,597,297 Corson et al May 20, 1952 

